Low-temperature NO-adsorption properties of manganese oxide octahedral molecular sieves with different potassium content

In this study, we synthesized hollandite-type manganese oxide octahedral molecular sieves (OMS) with different potassium content (KxMn8O16; K-OMS-2). Owing to crystal growth, the specific surface area of K-OMS-2 decreased with an increase in the K concentration for x > 1.5. The K-OMS-2 samples with x < 1.5 exhibited NO adsorption at low temperatures because of an oxidation reaction of NO. The amount of adsorbed NO depended on the oxidation activity of K-OMS-2 instead of the specific surface area (i.e., the number of NO adsorption sites). The amount of NO that was adsorbed at 323 K was correlated to the increase in the amount of oxygen released from K-OMS-2. It is assumed that the thermally unstable oxygen sites acted as oxidation sites for NO at low temperatures and thus increased the amount of adsorbed NO.